What is the ruling regarding the calculation of irrigation when distinguishing between costly and non-costly means is difficult?
Chapter on Zakat on Crops and Fruits
Al-Mughni
Book of Zakat
Primary text
When the exact measure of irrigation, the number of watering sessions, or the volume of water in each session is unknown, the ruling defaults to the dominant method. This is because meticulously calculating these factors is difficult and leads to excessive burden (*yashuqqu wa yata'addaru*). Therefore, the ruling follows the majority or predominant method, analogous to determining the valuation (*al-sum*) of livestock.
Supporting text
When the exact measure of irrigation is unknown, the obligation of the full Ushr (one-tenth) is assumed out of precaution (*ihtiyatan*). This is narrated from Ahmad in the narration of Abdullah. The basis is the obligation of the full Ushr, which is only waived by the confirmed presence of costliness (*kulfah*). Since the waiver is not established, the original ruling remains. Moreover, the default assumption is that there is no costliness for the majority of the period, so the presence of costliness cannot be established based on doubt.